1. Field of the Invention
The present disclosure relates to a hydraulic pump, and more specifically to a radial hydraulic pump with a variable eccentricity and delivery, intended to supply a hydraulic tool, such as jaws of life, conventionally used in the context of traffic accidents.
2. Description of Related Art
In the field of hydraulic tools, high pressures may be required due to the actions and other stress to be exerted. This is particularly true in the context of jaws of life, which may have to cut profiles or structures of large dimensions. In this context, a high nominal pressure, allowing the tool operation at its maximum power, is not permanently needed. Also, to be able to however use the tool in an entire range of pressures, multiple-stage pumps, and especially two-stage pumps, which provide the adapted pressure while allowing a hydraulic fluid delivery which is generally sufficient with the contemplated application, have been provided.
Despite the provision of such multiple-stage pumps, experience shows that the delivery may be insufficient, thus resulting in a limited actuation speed of the tool having said pump connected thereto. Now, in the context of the contemplated application, that is, in the specific context of the actuation of cutting tools, a higher speed enables to increase the efficiency of said tools.
To partly overcome such disadvantages, it has been provided to use radial hydraulic pumps, also called piston pumps, having a variable eccentricity, that is, for which the stroke of the pistons of said pump is not constant, but is capable of varying to optimally supply the hydraulic tool. Such hydraulic pumps enable to automatically and instantaneously vary the fluid delivery according to the pressure in the hydraulic circuit. Such a hydraulic pump is for example described in document EP 1 090 229. This hydraulic pump comprises a frame, a pump shaft capable of being rotated by a motor, around an axis which is stationary with respect to the frame, an eccentric sleeve engaged with the pump shaft and at least one stage of pistons arranged to be stationary with respect to the frame and radially extending in pump cylinders defining chambers. The eccentric sleeve is assembled on the pump shaft so that its rotation is blocked and so that it is shiftable along the axis of the pump shaft. Further, said sleeve is formed by an oblique cylindrical body which provides with an envelope surface a sliding surface for the pump pistons. Thus, the variable eccentricity is achieved by means of an element to settable in the axial direction and which appears in the form of an oblique cylindrical body.
Document EP 2 006 544 also describes a hydraulic pump of variable eccentricity. Said hydraulic pump comprises a frame, a pump shaft capable of being rotated by a thermal or electric motor, around an axis which is stationary with respect to the frame, an eccentric sleeve engaged with the pump shaft, and at least one stage of pistons arranged to be stationary with respect to the frame and radially extending in pump cylinders defining chambers. The eccentric sleeve is guided along an eccentric axis inclined with respect to the axis of the pump shaft, said eccentric axis having a cylindrical envelope surface, with a cone distance arranged parallel to the pump shaft axis, and a spring extending parallel to the eccentric axis ensures the displacement of the eccentric sleeve along the eccentric axis according to the load of the downstream circuit.
Such hydraulic pumps have the disadvantage of submitting the pump pistons to strong loads, whereby a complex and expensive adaptation of the pump pistons is necessary.
Further, such hydraulic pumps do not enable to reach a 700-bar pressure.